A source has linked blood and a knife found in a kidnapping suspect's car to Dru Sjodin (search), Fox News confirmed Monday.

The source close to the investigation of the missing University of North Dakota student said that a knife and blood matching the 22-year-old woman's type was found in the trunk of Alfonso Rodriguez Jr.'s (search) car. The source also said a knife sheath was discovered near Sjodin's car in the parking lot of the mall where she disappeared.

Allan Sjodin, Dru's father, said it was hard for him to hear the information, which was available in unsealed documents, but it didn't change his mission to find his missing daughter.

Sjodin, of Pequot Lakes, Minn., was last heard talking to her boyfriend on a cell phone on Nov. 22 after she left her job at a Victoria's Secret at the Grand Forks mall.

Rodriguez, 50, has been charged with kidnapping Sjodin. Evidence in the case, which was sealed by a judge after Rodriguez's arrest, should be released on Tuesday, the source said.

Rodriguez's maroon, four-door 2002 Mercury Sable was impounded by authorities before his Dec. 1 arrest in Crookston, Minn.

David Dusek, Rodriguez's public defender, has said that his client claims he had nothing to do with Sjodin's disappearance.

Police don't buy that story, but after three interviews Rodriguez was in isolation and refusing to talk to them further, Fox News learned.

The eighth-grade dropout was in trouble throughout the mid-1970s for crimes against women, and told a counselor he had a problem with women because he was sexually assaulted himself by an adult female when he was young.

There was word that Rodriguez's mother, who is very sick with cancer, wanted to speak to him, Fox News learned.

Rodriguez was interviewed by authorities last week, but has since declined to speak with investigators.

Bail has been set at $5 million, but Rodriguez has chosen to stay in jail because of fears for his safety. He faces a preliminary hearing Feb. 4 and arraignment on Feb. 6.

Rodriguez is a convicted rapist who has a history of attempted kidnapping with adult women, and has used a weapon in at least one assault. He was registered as a predatory offender, the classification for those believed to be at the highest risk of committing another sex crime.

Rodriguez was released from a Minnesota prison in May after serving 23 years for an attempted abduction in 1979. Wayne Swanson, who prosecuted Rodriguez, said Rodriguez tried to abduct a woman off the street, and stabbed her when she fought back.

Meanwhile, investigators said they planned to expand their search for Sjodin to areas south of Grand Forks this week.

Police Capt. Mike Kirby said searches would continue until officials have firm reason to believe Sjodin is dead.

"We are committed to this. The family is out and we will be out," Kirby said.

Searchers Monday included Sjodin's uncle, who noted that volunteers also were pitching in.

"Some of the guys we don't even know," Lowell Sjodin said. "It's this part of the country, I think. Everyone just pulls together."

Fox News' Catherine Donaldson-Evans, Carol McKinley and The Associated Press contributed to this report.